A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
The high pressure turbine drives the high pressure compressor through a high spool, and the low pressure turbine drives the low pressure compressor through a low spool. The fan section may also be driven by the low spool. A direct-drive gas turbine engine includes a fan section driven by the low spool, without a gear mechanism, such that the low pressure compressor, low pressure turbine and fan section rotate at a common speed.